A 25 percent increase in just the past month or so in the ­value of Hewlett-Packard Co.’s shares amounts to an “early holiday gift” that “investors should take advantage of,” says Topeka Capital, according to a Dow Jones report on Tuesday. Topeka, however, has downgraded the maker of personal computers to “sell,” with an $11.50 price target. The stock has been helped recently by short-covering after investors this year turned against the company, the firm said.